The present invention relates to an image forming apparatus and an image forming method using an electrophotographic process, such as a printer, a facsimile, or the like, and more particularly to an image forming apparatus and an image forming method having a double-side printing function for printing on both sides of a recording paper.
In a conventional image forming apparatus having such a double-side printing function, the processing described hereinunder are repeated. Namely, after finishing a printing on one side of a preceding recording paper, printing data on a next page are read from a higher rank apparatus to be printed on one side of a succeeding recording paper. Thereafter, printing data for the following page are read therefrom to be printed on the other side of the preceding recording paper. Thus, while printing is performed on one side of the succeeding recording paper, the preceding recording paper has to wait for a relatively long time in a state partly projected from a discharging port. Therefore, a problem is sometimes caused to occur inevitably in the conventional image forming apparatus having the double-side printing function. Namely, a user and so on sometimes pull out the paper in the above mentioned waiting state by mistake from the discharging port.
In order to avoid the problem, some methods have been employed in conventional image forming apparatus. Namely, in a first conventional image forming apparatus, a discharged paper receiving unit or a transfer path on which a recording paper is kept waiting after being printed on one side thereof is enlarged in size. Further, in a second conventional image forming apparatus, both side printing is never started on a succeeding recording paper until printing is completed on both sides of a preceding recording paper. Moreover, a third conventional image forming apparatus is disclosed in unexamined Japanese Patent Publication Hei1-279373, namely 279373/1992. In the third conventional image forming apparatus disclosed therein, a buffer memory for storing printing data from a higher rank apparatus is enlarged in capacity to increase the number of printable pages at a single time storage. Thereby, a printing time for each recording paper is shortened to reduce a waiting time for a recording paper mentioned above.
However, in the first conventional image forming apparatus, the enlargement of a size of the discharged paper receiving unit or the transfer path results in upsizing of the image forming apparatus itself. Further, the second conventional image forming apparatus in which both side printing is never stated on a succeeding recording paper until printing is completed on both sides of a preceding recording paper inevitably becomes slow in printing speed. Moreover, in the third conventional image forming apparatus disclosed in the above-mentioned publication, an increase of capacity of the buffer memory causes an increase of cost.